Cariogenic bacteria produce substance that aids calcium tolerance

BASEL, Switzerland: In a new study conducted at the University of Basel, researchers have investigated how cariogenic bacteria manage to survive in dental plaque, despite often hostile conditions. The results showed that the more calcium cariogenic bacteria dissolve, the greater the bacteria’s calcium tolerance and survival capability in the biofilm become.

In the caries process, cariogenic bacteria in biofilm cause calcium to diffuse out of the enamel. The dissolution of calcium increases the concentration of calcium locally, creating an environment that is hostile to bacterial life.

The researchers sought to understand how the bacteria tolerate high calcium levels and hypothesised that exopolysaccharides (EPSs) excreted by cariogenic bacteria support the species’ adaptation to local conditions by calcium binding. EPSs consist of insoluble sugar residues and form the biofilm’s scaffolding, ensuring that the bacteria remain adhered to the tooth surface.

The study results showed that EPSs play a central role in calcium tolerance of cariogenic bacteria in dental plaque by binding calcium. Additionally, the researchers demonstrated that EPSs possess a high number of calcium-binding sites through which they can integrate the free calcium into the biofilm, thereby neutralising toxic effects.

According to lead author Dr Monika Astašov-Frauenhoffer, from the university’s centre for dental medicine, this integration of calcium not only helps cariogenic bacteria to survive in the biofilm, but also causes caries. “EPSs’ integration of calcium inhibits the remineralisation of the enamel, as there is no longer sufficient free calcium present in the plaque. This discovery is important in gaining a better understanding of calcium regulation in caries.”

The study, titled “Exopolysaccharides regulate calcium flow in cariogenic biofilms”, was published in the PLOS ONE journal on 12 October.